1. Field of the Invention
The present invention relates to a speed change control system in a vehicular automatic transmission.
2. Description of the Prior Art
A vehicular automatic transmission is provided with a gear train using plural rows of planetary gear sets, and in which the constituent elements of the planetary gear sets are engaged and released selectively by frictional engaging elements to thereby attain a multiple speed range.
A hydraulic servo mechanism for operating each of the frictional engaging elements is controlled by a hydraulic controller, which in turn is controlled by an electronic controller.
In an automatic transmission having a multiple speed range, a plurality of speed change patterns can be set by selecting speed ranges suitably.
In Japanese Patent Laid Open Gazette No. 21562/1972 there is disclosed an apparatus provided with two kinds of speed change patterns, which are, three and four forward speed range drives of different gear ratios and the speed change patterns are changed over from one to another using a switch. Further, in Japanese Patent Laid Open Gazette No. 48652/1986 there is proposed a technique of changing over speed change patterns from one to another according to accelerator openings in an automatic transmission having six forward speed ranges attained by combining a main transmission having three speed ranges with an auxiliary transmission which attains an overdrive range and a direct drive range.
However, in the technique described in the above Gazette No. 48652/1986, it is provided with a speed change pattern for high throttle opening comprising a row of six forward speed ranges having 1st-1stA-2nd-2ndA-3rd-3rdA speed ranges including 1st-2nd-3rd speed ranges of main transmission speed ranges with the auxiliary transmission serving as a direct drive range and 1stA-2ndA-3rdA speed ranges with the auxiliary transmission serving as an overdrive range (indicated by "A"), and a speed change diagram for controlling the change of speed between the speed ranges at a throttle opening larger than a preset throttle opening value .theta..sub.0 ; and a speed change pattern for low throttle opening comprising a row of four forward speed ranges having 1st-2nd-3rd-3rdA speed ranges of three main transmission speed ranges with the auxiliary transmission serving as a direct drive range plus the third speed range (3A) of the main transmission with the auxiliary transmission serving as an overdrive range, and a speed change diagram for controlling the change of speed between the speed ranges in a throttle opening smaller than the aforementioned preset value .theta..sub.0. Further, when the throttle opening is larger than the preset value .theta..sub.0, the speed change pattern of the six forward speed ranges described above is selected, while when the throttle opening is smaller than the preset opening, the speed change pattern of the four forward speed ranges referred to above is selected. Therefore, at the time of change-over from the speed change pattern for low throttle opening to the speed change pattern for high throttle opening, the change-over may be done in the same speed range. At the same vehicle speed, however, since the throttle opening in the speed change pattern for low throttle opening is larger than that in the speed change pattern for high throttle opening, a speed change shock may occur at the time of pattern change-over, which may impair the shift feeling.